Pfizer Vaccine Still Very Effective Against Coronavirus Variant Despite Small Window of Risk

Waldo Swiegers/Bloomberg via Getty Images

The coronavirus variant first detected in South Africa may overcome some of the protection the Pfizer-BioNTech vaccine offers, but infections in vaccinated people are still rare.These breakthro…

Waldo Swiegers/Bloomberg via Getty Images
  • The coronavirus variant first detected in South Africa may overcome some of the protection the Pfizer-BioNTech vaccine offers, but infections in vaccinated people are still rare.
  • These breakthrough infections can occur with any vaccine. They're not an indication that they're ineffective.
  • Laboratory studies suggest this variant may also be able to evade the neutralizing antibodies that result from vaccination.

The coronavirus variant first detected in South Africa may be able to evade some of the protection offered by two doses of the Pfizer-BioNTech COVID-19 vaccine, according to a new preprint study based on real-world data in Israel.

However, the authors point out that in spite of this ability, the rate of this variant in Israel remains very low.

In addition, no infections caused by this variant occurred in people 2 weeks or more after they received their second dose.

The authors write that this suggests that the transmission of concerning variants can be controlled with high vaccination rates and precautions, such as masking and physical distancing.

Low risk of infections in vaccinated people

Clinical trials show that the Pfizer-BioNTech COVID-19 vaccine has a very high efficacy — 95 percent — against symptomatic infection.

Real-world studies show a similar high effectiveness against all infections, including asymptomatic ones.

So, very few people fully vaccinated with this vaccine will contract the coronavirus. However, breakthrough infections can occur. This is true of all vaccines.

“No vaccine is 100 percent effective for every recipient, so we will continue to see rare infections in people who have been vaccinated,” said Dr. S. Wesley Long, an associate professor of pathology and genomic medicine at Houston Methodist, who was not involved in the new study.

“But many times these infections are mild, and the protection against severe disease and hospitalization is still very robust,” he said.

In the new study, researchers at Tel Aviv University analyzed PCR samples collected from nearly 400 people who developed a coronavirus infection after receiving one or both doses of the Pfizer-BioNTech vaccine.

Researchers compared these PCR samples with samples taken from a similar group of unvaccinated people.

They looked at whether vaccinated people were more likely to contract an infection with one of the coronavirus variants, compared with the original coronavirus.

They focused on the variant first detected in South Africa (B.1.351) and the variant first detected in the United Kingdom (B.1.1.7), both of which are present in Israel.

These variants are concerning because they transmit more easily among people than earlier variants of the virus. B.1.1.7 is also suspected of causing more severe COVID-19, although a recent study suggests this may not be the case.

Laboratory studies suggest that B.1.351 may also be able to evade the neutralizing antibodies that result from vaccination with one of the current vaccines.

The study was published April 9 on the preprint website medRxiv. It has not yet been peer reviewed and was a small study, so the results should be viewed with caution.

Variants ‘break through’ partial vaccine protection

The Israeli researchers found that most of the infections in vaccinated people were due to the B.1.1.7 variant, which is the dominant variant in the country.

In contrast, B.1.351 was present in less than 1 percent of the samples the Israeli researchers examined.

In the United States, B.1.1.7 is also the dominant variant, with B.1.351 making up a very small number of cases.

In the study, among partially immunized people — between 14 days after the first dose and a week after the second dose — infections with B.1.1.7 were more common, compared with unvaccinated people.

This suggests that B.1.1.7 is able to overcome the partial protection offered by the vaccine in the few weeks after the first dose. Pfizer and BioNTech recommend that the doses be given 3 weeks apart.

This partial protection against B.1.1.7 during this time “might explain why during the early stages of the vaccination rollout in Israel, it took a while till vaccination effects were noted and cases began to drop,” study author Adi Stern said on Twitter.

Until enough people had developed full protection from the vaccine, a large number of infections caused by B.1.1.7 could still occur among the vaccinated portion of the population.

In contrast, among fully vaccinated people in the study — at least 1 week after the second vaccine dose — infection with B.1.351 was more common, compared with unvaccinated people.

Based on this, “we see evidence for reduced vaccine effectiveness against the [South Africa] variant,” wrote Stern on Twitter, “but [this variant] does not spread in Israel.”

The lack of spread of this variant in Israel may be due to the high effectiveness of the Pfizer-BioNTech vaccine coupled with other precautions such as masking and physical distancing, the researchers wrote in their paper.

It’s also possible that the B.1.1.7 variant — which has a high transmission rate — may outcompete B.1.351, they added.

“Overall, the study shows there is excellent protection against the B.1.1.7 variant after two doses,” Long said, “and that while there is an increased risk of breakthrough by B.1.351, these breakthroughs are incredibly rare.”

Vaccination, masking, and distancing can control variants

In spite of B.1.351’s potential ability to break through the vaccine’s protection, infections caused by this variant occurred only during a “short window of time,” wrote Stern — none occurred 14 or more days after people received their second vaccine dose.

This fits with other studies that suggest full immunization doesn’t occur until after that point.

However, there were a small number of infections caused by B.1.351 in the study, so additional research is needed to confirm the long-term vaccine protection against this variant.

Pfizer is also researching a COVID-19 vaccine booster that targets variants such as B.1.351.

Long said while the results of the new study are worth paying attention to, they're not that concerning.

“The infections after complete vaccination were very rare,” he said, “and in the case of B.1.351, we are not seeing [this variant] spread well outside of South Africa.”

“If anything, these findings demonstrate the need to vaccinate as many people as quickly as possible to reduce transmission,” he added, “as well as the need to continue our nonpharmacologic measures like masking and [social] distancing to help reduce transmission.”