COVID-19 Vaccine Generic Pfizer Bottle

Fort Belvoir Community Hospital sets up a COVID-19 vaccination clinic at the Community Center. 

Nearly 30 percent of all Virginia residents have received at least one dose of COVID-19 vaccine, according to the Virginia Department of Health, and nationwide, the number of people who have received at least one dose is nearing 150 million — roughly 47 percent of the overall population. 

Still, experts don’t yet know exactly when our nation will reach the magic number of inoculations to achieve herd immunity and end the pandemic altogether. But the science is rapidly evolving and the results from studies into the vaccines continue to improve our understanding of how well the vaccines work.

While experts don’t yet know how long vaccine immunity will last — and therefore whether the COVID-19 shot will become an annual vaccine, like the flu shot — there’s a lot they have learned in the past few months.

Here’s the latest on what we know about the vaccines available in the US:

Moderna and Pfizer vaccines could be 90% effective against SARS-CoV-2 infection 

Just this Monday, researchers at the US Centers for Disease Control and Prevention released the results of a study of 3,950 US health care workers, first responders and other essential workers. The study looked at the effectiveness of the Moderna and Pfizer vaccines against infections of SARS-CoV-2 (the virus that causes the COVID-19 illness). While the clinical trials showed both vaccines were effective at preventing disease caused by SARS-CoV-2, the new results from this study indicates that the vaccines are also effective at preventing the infection in the first place. 

This is highly significant because it could mean the vaccines are effective at preventing transmission.

One dose of Pfizer vaccine could be enough to protect against “silent COVID” 

Preliminary research published in early March by a group of researchers at the University of Cambridge in the UK suggests that a single dose of the vaccine manufactured by Pfizer-BioNTech reduced instances of asymptomatic coronavirus infections by a factor of four. Researchers analyzed the results of nearly 8,900 COVID-19 tests taken by health care workers in the UK. The results have not yet been peer reviewed.

Pfizer vaccine is 94% effective in the real world

An Israeli study found that 7 days or more after the second shot, the two-dose Pfizer vaccine was 94 percent effective against COVID-19 disease and 92 percent effective against severe disease. The results, consistent across all age groups, were also tested at a time when the more deadly British variant (B.1.1.7) was circulating in Israel, suggesting the vaccine is effective at preventing disease from that variant, too.  

mRNA vaccines may be less effective against South Africa variant B.1.351

Researchers in France published the findings of a small-scale study of SARS-Co-V-2 antibodies against viral variants. The results showed that antibodies from people who had recovered from the virus were reduced by 60% after nine months. Antibody levels from fully vaccinated individuals were 14 times lower against the B.1.351 variant than against the original strain. The authors said their study indicates that the B.1.351 variant “may increase the risk of infection in immunized individuals.”

Moderna said in early February that there was a “sixfold reduction” in its vaccine’s effectiveness against the South Africa variant.

And here's what we know about 'natural' immunity:

People over 65 are more likely to get COVID-19 twice

A team of researchers in Denmark scoured millions of COVID-19 test results and found that six months after infection, antibodies against the virus were 80 percent effective. However, that number was 47 percent in individuals over 65, significantly lower than the aggregate. 

Antibodies last up to several months

Two different studies, one in Wuhan, China and the other in France, indicate that antibodies begin to disappear nine months after a COVID-19 infection. 

The Chinese study took blood samples from more than 9,500 people and found that of them, only 7 percent had been infected with the virus. Of those that had been infected, 80 percent had been asymptomatic and only 40 percent had detectable antibodies. 

The French study took blood serum samples from 58 individuals who had recovered from COVID-19. Of those 58 serum samples, those from individuals who had recovered within the previous nine months were able to stave off infection. However, those that had been infected more than nine months prior were less successful, with only 40 percent of the samples being able to neutralize the South Africa variant (B.1.351).

The body’s immune system remembers how to make antibodies for at least six months

According to research conducted at Rockefeller University in New York City, once an individual has recovered from a COVID-19 infection the number of immune cells programmed to make antibodies, called memory B cells, remain in the body for at least six months. This means that even if the antibodies themselves are no longer active, the memory B cells would kick in to produce more antibodies if the immune system were reinfected. 

For now, the CDC continues to urge caution 

The U.S. CDC discourages medium- or large-sized gatherings and to follow state and local guidelines. In Virginia, the Governor’s Office released guidance last week that relaxed some restrictions, but didn’t completely lift them. 

  • The maximum number of people allowed at a social gathering is now 50, and the maximum number of people allowed to gather outdoors is 100. 
  • Indoor and outdoor entertainment and public amusement venues may operate at 30 percent capacity.
  • The Governor’s Office has said that spectators at recreational sporting events should not exceed 100 people or 30 percent capacity indoors, whichever is less. Outdoor sporting events should not have more than 500 spectators. 

As for safety of gathering privately in households, the CDC has issued the following guidance.

Vaccinated households can mingle together

The CDC has determined that the risk of COVID-19 transmission is very low among fully vaccinated adults who are not wearing masks or social distancing. “For example,” the website says, “if you are fully vaccinated, it is likely a low risk for you to invite other fully vaccinated friends to dinner inside your private residence.”

A vaccinated household can mingle with one unvaccinated low-risk household 

The CDC continues to recommend that vaccinated and unvaccinated individuals alike wear masks in public to prevent the spread of COVID-19. However, the CDC has recently said that “if the unvaccinated people are from a single household that does not have individuals at risk of severe COVID-19, they can visit with fully vaccinated people indoors, without anyone wearing masks, with a low risk of SARS-CoV-2 transmission.” 

That means fully vaccinated grandparents can visit their unvaccinated healthy children and healthy grandchildren without wearing masks or physical distancing as long as none of the individuals involved are at risk for severe COVID-19.

If any of the unvaccinated individuals at a private gathering are at risk for severe COVID-19, all attendees should practice social distancing, wear a well-fitting mask and make sure they are in a well-ventilated space.

For more information on the latest guidelines, visit the website for the Centers for Disease Control and Prevention at


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