Rep. Stephen Lynch tested positive for COVID-19 Friday despite having received both doses of the Pfizer vaccine, his office announced.

According to a statement from the Democrat’s spokeswoman, Molly Rose Tarpey, Lynch “had received the second dose of the Pfizer vaccine and subsequently received a negative COVID-19 test prior to attending President Biden’s Inauguration. While Mr. Lynch remains asymptomatic and feels fine, he will self-quarantine and will vote by proxy in Congress during the coming week.”

On Thursday, Lowell-area Rep. Lori Trahan announced she had tested positive, about a week after receiving the first dose of the vaccine.

Lynch is 65; Trahan is about two decades younger.

Dr. Cassandra Pierre, the Medical Director of Public Health Programs and Epidemiologist at Boston Medical Center, says even though each dose provides some level of immunity, people need to wait about two weeks after receiving their second dose of both the Pfizer and Moderna vaccines to achieve optimal immunity from the virus.

She added that both vaccines have a 95-percent efficacy rate, which means some people — even after waiting those two weeks — may still become infected with the virus.

“But, what we’ve been seeing, by and large, is the very few people who become infected after that second dose have mild illness, and we presume that the majority will have a much milder illness than they would have otherwise experienced had they not been vaccinated,” said Pierre.

Pierre said these cases shouldn’t dissuade others from getting vaccinated in the first place.

“The amount of people who would be at risk for becoming infected after that second dose will drop as we begin to see our community levels of COVID drop as well,” said Pierre. “So please don’t lose hope. These vaccines do work.”