There has been some research that suggests the Pfizer/BioNTech vaccine provides some protection after one dose.

Researchers at Israel’s largest hospital looked at what happened after 7,000 staff got vaccinated with the first dose of the Pfizer/BioNTech vaccine. By the second to fourth week after they got the first shot, rates of symptomatic infection were down by 85%.

By Jan 24, 2021, of the 9109 eligible staff, 7214 (79%) had received a first dose and 6037 (66%) had received the second dose. 5505 (91%) fully
vaccinated HCWs received the second dose on days 21 or 22 after the
first dose. 6818 (95%) HCWs were vaccinated at Sheba Medical Centre.
All employees vaccinated in the community (n=396) were required to report dates of first and second dose to the Human Resources department at
Sheba Medical Centre.

Overall, there were 170 SARS-CoV-2 infections among HCWs in the
period between Dec 19, 2020, and Jan 24, 2021, of which 99 (58%)
HCWs reported symptoms and were designated as COVID-19 cases. Of the 170 HCWs who became infected, 89 (52%) were unvaccinated, 78 (46%) tested positive after the first dose, and three (2%) tested positive after the
second dose. Among the 125 infections that could be traced, 87 (70%) were
community acquired and there were no nosocomial clusters.

Compared with a SARS-CoV-2 infection rate of 7·4 per 10 000 persondays in unvaccinated HCWs, infection rates were 5·5 per 10000 person-days and 3·0 per 10 000 person-days on days 1–14 and 15-28 after the first dose of the vaccine, respectively.

Adjusted rate reductions of SARS-CoV-2 infections were 30% (95% CI 2–50)
and 75% (72–84) for days 1–14 and days 15–28 after the first dose,
respectively. Compared with a symptomatic COVID-19 rate of 5·0 per 10000 person-days in unvaccinated HCWs, disease rates were 2·8 and 1·2 per 10000 person-days on days 1–14 and days 15–28 after the first dose of the
vaccine, respectively. Adjusted rate reductions of COVID-19 disease were 47% (95% CI 17–66) and 85% (71–92) for days 1–14 and days 15–28 after the
first dose, respectively.